In the process, the Nevada Democrat renewed his call for the presumed GOP presidential nominee to share more information about his taxes.

Reid has been pressuring Romney to release his returns, in part by claiming to have learned from an inside source that Romney did not pay federal taxes.

On Thursday afternoon, Romney responded vigorously, arguing in an interview on Fox News Radio that Reid needed to provide proof of his claim.

&ldquo;It&rsquo;s time for Harry to put up or shut up,&rdquo; he said.

This evening, Reid responded by saying the onus is on Romney.

&ldquo;When it comes to answering the legitimate questions the American people have about whether he avoided paying his fair share in taxes or why he opened a Swiss bank account, Romney has shut up. But as a presidential candidate, it&rsquo;s his obligation to put up and release several years&rsquo; worth of tax returns just like nominees of both parties have done for decades," he said in a statement.

This week, Reid has been telling reporters that an unnamed source associated with Romney&rsquo;s former company, Bain Capital, told him that Romney paid nothing in federal income taxes for 10 years.

In the Fox News Radio interview, Romney said that the claim is &ldquo;totally and completely wrong&rdquo; and that he believes it is politically motivated.

&ldquo;I&rsquo;m looking forward to have Harry reveal his sources, and we&rsquo;ll probably find out it&rsquo;s the White House,&rdquo; he said.

After pressure from opponents in the Republican primary, Romney released his 2010 tax returns and a summary of his 2011 tax returns earlier this year. He has pledged to release the final version of his 2011 tax returns but nothing more, saying the other records would be distorted by Democrats in attack ads.